1. Field of the Invention
The present invention relates to a process for producing a liquid crystal display device using an excellent resist peeling liquid for forming a thin film pattern of an electrically conductive circuit and an insulator, and also using a process for peeling a resist with the resist-peeling liquid.
2. Description of the Related Art
As a process for producing an electronic device such as a liquid crystal display device, a semiconductor device, or any of various circuit base plates, there has been well known to those skilled in the art a process which comprises forming a thin film by sputtering or the like, forming a predetermined pattern on the thin film by the use of a photoresist by photolithography, removing unnecessary portions by etching, peeling off the photoresist and repeating the above procedure, thereby producing a product. In the case of a thin film transistor-liquid crystal display (referred to hereinafter as TFT-LCD) device which is a representative liquid crystal display device, a TFT substrate is produced by forming gate electrodes on a glass substrate through the steps of sputtering, photolithography, etching and resist-peeling; forming a gate-insulating film and amorphous silicon (a-Si) transistors through the steps of chemical vapor deposition (CVD), photolithography, etching and resist-peeling; forming indium tin oxide (ITO) electrodes through the steps of sputtering, photolithography, etching and resist-peeling; forming source and drain electrodes through the steps of sputtering, photolithography, etching and resist-peeling; and forming a passivation film through the steps of CVD, photolithography, etching and resist-peeling. The TFT substrate is laminated to a color filter substrate to seal up a liquid crystal in the gap between the TFT substrate and the color filter substrate to produce a color display. In such a series of steps, it is absolutely necessary that the photoresist-peeling step be perfect. Therefore, various proposals have been made for a resist-peeling liquid used for efficiently peeling a resist.
For example, JP-A-57-165834 discloses an amine type resist-peeling liquid, and JP-A-62-35357 discloses a phenol type resist-peeling liquid.
The above resist-peeling liquids are well known to those skilled in the art but involve the following problems in practical application.
An explanation is given below by taking the case of a novolak positive resist which is most generally used as a photoresist. In processes for producing various electronic devices, a resist formed on a substrate is irradiated with ultraviolet light through a predetermined mask, after which the exposed portion is removed by development, and the remaining resist is used as an etching resist. Concrete etching conditions vary depending on a substance to be etched, and etching types usable in this case are roughly classified into two classes: wet etching utilizing an electrochemical reaction in a solution, and dry etching utilizing the reaction of a radical in a gas phase.
Depending on the etching conditions of these processes, complicated chemical reactions are often caused on the surface of the resist. The change in quality of the surface layer of the resist by the reactions brings difficulty in completely peeling off the photoresist by the use of a conventional resist-peeling liquid. The incomplete peeling leaves a resist residue on the pattern or between the patterns formed by etching. Even when the amount of the residue is very small, the residue is a great factor causing defects such as burnout, short circuit, etc. in the subsequent steps such as film formation, photolithography, etching, etc. These defects decrease the reliability and yield of a product and hence cause inestimable losses in performance characteristics and economical benefit.
The above-mentioned conventional peeling liquids cannot cope with such a problem. In addition, there has been no method capable of solving such a problem and the problem of change in quality of the resist surface caused depending on various etching conditions, at the same time. Therefore, for coping with these problems, there has been no choice but, for example, to elongate the resist-peeling time, depending on etching conditions.
The present invention is intended to provide a resist-peeling liquid of extremely high performance which can completely peel the resist having a portion of which the quality has been changed during the above-mentioned etching process and does not leave the residue to the subsequent steps, and a process for peeling a resist by the use of the resist-peeling liquid.
In addition, since the above-mentioned conventional peeling liquids have a complicated composition, it has been very difficult to separate a resist from the peeling liquid after being used for peeling the resist, recover the peeling liquid and regenerate the same. Due to the complicated composition, even when a general separating method (e.g. distillation) is employed, a liquid recovered by distillation has a composition different from that of the original peeling liquid. Therefore, there has been no choice but to readjust the composition of the recovered liquid after analysis for its components. Such regeneration imposes a heavy economic burden, and disposal of the peeling liquid by a method such as incineration has been easier than the regeneration.
However, since it is obvious that the disposal by incineration of a large amount of the resist-peeling liquid composed mostly of one or more organic solvents has an undesirable influence on the global environment, it has been desired to develop a resist-peeling liquid which is free from the above problems and easy to recover and regenerate.
A first object of the present invention is to provide a process for producing a liquid crystal display device using the above-mentioned excellent resist-peeling liquid and using a process for peeling a resist with the resist-peeling liquid.
A second object of the present invention is to provide the aforesaid resist-peeling liquid which is easy to recover and regenerate.
A third object of the present invention is to provide a process for most effectively regenerating the above resist-peeling liquid easy to regenerate.
A fourth object of the present invention is to provide a peeling process suitable to the resist-peeling liquid of the present invention.